Definition: The recording instrument is defined as the instrument which records the continuous variation of the magnitude of an electrical quantity for a particular period. It is used in a placed where the continuous reading of circuit conditions is required. The record is used for future reference or computational work.
The recording instruments take readings of the physical quantities in the form of the graph. It also records the variation of the quantities concerning the time. The voltmeter, thermoscope, ECG machine, galvanometer recorder are the examples of the recording instrument.
The indicating instrument records a continuous reading, but they require an observer for continuously observing the variations in readings. The example of the recording instrument is obtained by improving the construction of an indicating instrument. The indicating instrument is converted into a recording instrument by replacing their pointer with the light arm ink pen.
The ink pen is deflected for recording the readings on the graph paper. The pen is continuously rotated on the drum at the constant speed. The path traced by the pen gives a continuous reading of the variant physical quantity.
The magnitude of the quantity is read from the traced chart. The instruments are used in the power stations where continuous reading is required.